1. Technical Field
The present disclosure relates to a floating structure with an on-deck fuel tank, and more particularly, to a floating structure with an on-deck fuel tank which is covered to seal the fuel tank so that the fuel tank is not exposed to air, thereby enhancing safety.
2. Description of the Related Art
Recently, in order to solve environmental problems such as global warming, environmental pollution, and the like, regulations for carbon emission are being actively discussed all over the world. Also, environment-friendly logistics such as low-carbon green growth have been proposed in Korea.
In shipbuilding fields, a large amount of carbon dioxide is emitted by the use of existing fossil fuel. Therefore, many efforts have been made to reduce carbon dioxide emission.
Generally, various ships such as bulk carriers, container ships, crude oil carriers, passenger ships, and the like have employed a fuel supply system using heavy oil (HFO) or diesel oil (MDO), for example, bunker C oil, which is liquid fuel, as propulsion fuel.
In the conventional fuel supply system, if heavy oil or the like used as fuel is combusted, serious environmental pollution is caused due to various harmful substances contained in the exhaust gas. As the prevention of environmental pollution is increasingly demanded worldwide, regulations for propulsion systems using heavy oil as fuel oil have been reinforced. As a result, costs for meeting these regulations have been gradually increased.
Also, if oil prices are considerably increased by factors such as depletion of fossil fuel, localized unrest, or the like, several operational problems such as the rapid increase of fuel expenses of ships using heavy oil as fuel, etc., will be caused.
Thus, technologies for using liquefied fuel gas that is environment-friendly fuel as fuel of ships have recently attracted attention. The term “liquefied fuel gas” as used herein represents gaseous fuel, such as LNG, LPG, CNG, DME, or the like. The liquefied fuel gas exists in a liquid or gas state when being stored in a fuel tank, but exists in a gas state when being fed to a propulsion system.
Liquefied Natural Gas (LNG) is generated by liquefying natural gas collected from a gas field. The main component of LNG is methane. LNG is advantageous in terms of space efficiency because its volume is reduced to about 1/600 when being liquefied by lowering its temperature or applying a pressure. However, since LNG has a low boiling point of about −162° C., LNG needs to be loaded into a specially insulated tank or container and be kept below a boiling point during transportation and storage.
Liquefied Petroleum Gas (LPG) is generated by cooling and liquefying heavy hydrocarbon (two or more carbon atoms) component generated at the time of collecting crude oil from an oil field or purifying crude oil or heavy hydrocarbon component collected together at the time of collecting natural gas at a relatively low pressure (about 6 kg/cm2 to about 7 kg/cm2). LPG is advantageous in terms of storage and transportation because the volume thereof is reduced to about 1/250 during liquefaction. The main component of LPG is propane and butane, and LPG may contain a small amount of ethane, propylene, butylen, or the like.
Compressed Natural Gas (CNC) is generated by compressing natural gas at about 20 MPa so as to use the natural gas as fuel.
Dimethyl Ether (DME) is a kind of ether and has lower flammability and less toxicity than LPG. Also, DME has a small environmental load because a small amount of exhaust fume is generated during the combustion due to high oxygen concentration.
When LNG is used as fuel of ships among the above-described liquefied fuel gases, carbon dioxide emission of LNG is about 20% smaller than that of petroleum-based fuels such as diesel oil, bunker C oil, or the like. Furthermore, since nitrogen oxide and sulfur oxide, which are the main cause of air pollution, are not almost exhausted, LNG can be used as an environmental-friendly fuel.
In case of LNG carriers, much discussion has been made about technologies for duel fuel engines using boil-off gas (BOG). Also, much discussion has been made about technologies that utilize liquefied fuel gas, including LNG, as propulsion fuel for ships. However, these technologies are still in the early stage of development.
In general, since liquefied fuel gas such as LNG is lower in density than liquid fuel such as HFO, a fuel tank is inevitably increased in volume as compared with the case where only liquid fuel having relatively high density is used as fuel. Thus, in the case where a fuel tank for liquefied fuel gas is installed in a ship, a space for accumulating cargo may be reduced as compared with the case where a fuel tank for liquid fuel such as HFO is installed.
To solve this problem, when the consumption of fuel is small, detachable fuel tanks may be used such that some of plural fuel tanks are removable, or a fuel tank may be installed on a deck of a floating structure.